Subject: [Isis-wg] MD5 Authentication Questions

From: "Suresh Boddapati" <[email-masked]>
Date: Thu, 31 Jan 2002 01:10:46

Per the "IS-IS Cryptographic Authentication" draft,
"When LSPs are authenticated, the Checksum and Remaining Lifetime fields are 
set to zero before authentication is computed".

1)Is the Remaining Lifetime field set back to the original value after 
computing the authentication?

2)What about the checksum? Is it left at zero since the authentication value 
itself can be used as a mechanism to detect packet corruption? In other 
words, should the checksum field be always zero for MD5 authenticated 
packets? If not, is the checksum computed after adding the authentication 
information to the LSP or before?

Thanks in advance.

Regards,

Suresh

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From: Tony Li <[email-masked]>
Date: Wed, 30 Jan 2002 17:54:07 -0800

| Per the "IS-IS Cryptographic Authentication" draft,
 | "When LSPs are authenticated, the Checksum and Remaining Lifetime fields are 
 | set to zero before authentication is computed".
 | 
 | 1)Is the Remaining Lifetime field set back to the original value after 
 | computing the authentication?
 | 
 | 2)What about the checksum? Is it left at zero since the authentication value 
 | itself can be used as a mechanism to detect packet corruption? In other 
 | words, should the checksum field be always zero for MD5 authenticated 
 | packets? If not, is the checksum computed after adding the authentication 
 | information to the LSP or before?

Both values should be restored after computation.

Tony